Traditionally, machining methods such as turning, grinding, drilling, and milling involve application of mechanical forces. In these methods, a hard tool is used to machine the workpiece, and thus, the tool needs to be harder than the workpiece. However, in some applications, it is desirable that the workpiece itself be made of hard materials. For example, blades of turbine engines have stringent requirements including hardness since they are subjected to harsh operating environments. When the workpiece itself is hard, conventional mechanical machining is typically not feasible.
Electrochemical machining (ECM) is commonly used as an alternative method of machining hard workpieces. In ECM, an electrically conductive hard workpiece is machined with a tool, which is also electrically conductive. During ECM, the tool acting as a cathode is located relative to the workpiece acting as the anode, such that a gap is defined therebetween, and the gap is filled with flowing electrolyte such as sodium nitrate aqueous solution. A high density direct current with low voltage is applied between the cathodic tool and the anodic workpiece to cause electrolytic dissolution of the workpiece. The dissolution action takes place in an electrolytic cell formed by the cathodic tool and the anodic workpiece separated by the flowing electrolyte. The eroded material or sludge, a form of metal hydroxide, is removed from the gap with the flowing electrolyte. The anodic workpiece generally assumes a contour that matches the contour of the cathodic tool. The sludge can be filtered from the electrolyte and the clean electrolyte can be reused.
In ECM, the tool does not wear. Also, the rate of machining is independent of the hardness of the workpiece. Thus, soft metals such as copper and brass may be used as the tool to shape workpieces of hard or tough metals such as carbon steel, inconel, titanium, hastelloy, and kovar or alloys thereof, and the tool cathode may be used repeatedly. This is advantageous since shapes, even complex ones, can be formed on soft metals with relative ease and used to shape workpieces of hard metals and alloys.
ECM does have its drawbacks. Specialized tool must be constructed for each desired shape in the conventional ECM. In an industry like power generation, even a small gain in efficiency such as one percent represents significant operation cost savings. Thus, turbine manufacturers are constantly redesigning turbine blades and other turbine parts to achieve incremental efficiency gains. Using the conventional ECM in such a circumstance requires regularly producing new tools, which can be very expensive. Thus, it would be desirable to provide electrochemical processing methods, apparatuses, and systems that can flexibly adapt to workpieces of different shapes to reduce costs and time associated with the conventional ECM.